With the development of society and science technology, the automobile as an indispensable social transport plays a more and more important role in people's work and life. Currently, high-load, high-speed and environmental protection have become the development direction of the automotive industry. However, the technical problems brought by high-load and high-speed of the automobile have not been solved yet, and one of the difficult problems is the automotive brake problem.
The automotive brake is virtually the process in which kinetic energy of the moving automobile is converted to heat energy. The main problem of the brake pad in high-speed and high-load conditions is the failure of the material at high temperatures. People have tried to modify phenolic resin which is used as a binder in the brake pad to improve the heat resistance of phenolic resin, in order to solve the failure problem of the material at high temperature. For example, JP11286676 (A) discloses a method of applying aromatic compounds modified phenolic resin in brake pads. JP10007815 (A) discloses a method of applying a mixed system of rubber modified phenolic resin and ordinary phenolic resin in brake pads. JP2001247640 (A) discloses a method of applying bismaleimide modified phenolic resin in brake pads. Although the performance of the friction materials obtained by the three methods has been improved to some extent, the problem of the failure of materials at high temperature has not been fundamentally resolved.
Taking effective manner to promptly conduct out the heat generated by braking becomes the key to avoid the failure of the brake pad materials at high temperature. When braking, the braking system is expected to provide friction force as great as possible, so that the automobile can be braked in the shortest distance within the shortest time. However, on the other hand, if the friction force is too large when braking, it is very easy to cause lock phenomenon. The greater the friction force is, the faster the rate of heat energy generates, the more serious the heat energy accumulates on the friction surface when braking, and the more easily the material fails.
Currently, many high-end cars use the ABS (anti-lock braking system), ABS can achieve “inching braking” in a high frequency, which can effectively prevent the lock phenomenon due to the high coefficient of friction. On the other hand, the frictional heat can be quickly dispersed in the intervals of inching braking, so that the brake pad materials can be better protected from failure at high temperature. In order to meet the effect of ABS inching braking on the protection materials, a kind of brake pad with high thermal conductivity is required, so as to disperse the heat of the surface of the brake pads in the intervals of inching braking.
Carbon has many advantages such as excellent heat resistance, high thermal conductivity and chemical inertness, which serves as an important structural material and functional material, and is widely used in metallurgy, chemical industry, machinery, electronics, aviation and other fields. Applying the carbon materials in the friction materials can significantly increase the thermal conductivity of the friction materials, so that the brake heat can be conducted out to avoid the failure of materials due to local heat accumulation of the friction surface, moreover, the carbon materials can play an enhanced role. JP2008223781 (A) discloses a method of adding carbon nanofibers into friction materials. EP1357310 (A) discloses a friction material composite containing coated reinforcing fibers comprising carbon and whose matrix comprises silicon carbide. The friction material has high thermal conductivity and good frictional properties at high temperatures. CN98105056.5 discloses a semi-metallic non-asbestos brake pad adding carbon fiber, and the inventive product has high thermal conductivity, smooth braking, wear-resistant and high service life. EP1028098 (A) discloses a friction material prepared by carbon fiber reinforced carbon/carbon composite material suitable for high-speed and high-load. KR100878945 (B1) disclosed a method of coating carbon nanotubes on the surface of the finished brake pads. The brake pads prepared by the method have good thermal conducting property, uniform temperature distribution on the braking surface, high adhesion and good material stability. Although the above methods of adding carbon materials to the friction materials can improve the thermal conductivity of friction material and significantly improve the friction and wear properties of the material, the production costs of the carbon material are very high, which limits its practice use.